Fluids (e.g., liquids and gases) can be conveyed through subsea pipes for long-distance transportation and distribution. The surrounding marine environment can expose the pipes to a variety of, and sometimes relatively aggressive, service conditions and it can cause leaks to form in the pipes. For example, pipes can be breached due to mechanical forces (e.g., impact from other equipment or remotely operated vehicles (ROVs) during operation, fatigue from motion water, etc.), corrosion, or other surrounding conditions. Pipes can be monitored for leaks in order to prevent pipe damage and deterioration, for example, in order to comply with environmental regulations.
In order to control flow within a network of pipes, pressure can be measured at a variety of locations. In general, a pressure measurement can be performed by placing a pressure sensor in contact with the fluid. The sensor can include a sensing element that moves in response to changes in fluid pressure, and the sensor can convert the movements into another type of output (e.g., mechanical, electrical, etc.) that can be calibrated to provide a measurement of the fluid pressure.
In subsea oil installations and processing facilities, pressure measurements can be obtained at a location remote from the location where the measurement is desired. In one example, long lines containing a transmission fluid, such as a hydraulic oil, can be employed to communicate the pressure of a process fluid to a remote pressure gauge. A seal can be used to separate the process fluid to be measured from the transmission fluid flowing through the lines. The seal can transfer the pressure from the process fluid to the transmission fluid, which in turn can transfer the pressure of the process fluid to the pressure gauge at the remote location. Even under circumstances where a pressure sensor is positioned very close to the location of the process fluid, there can be a distance between a location where the process fluid enters the pressure sensor and a sensing element that measures the pressure. For example, a hydraulic differential pressure sensor operates under the same principles as discussed above, except that the length of the lines containing the transmission fluid are shorter.
These distances separating the fluid under pressure from the sensing element of the pressure sensor can present challenges for pressure measurements in subsea oil installations and processing facilities. In general, the diameter of the lines carrying the transmission fluid can be small compared to the diameter of a pipe carrying the process fluid. While the total volume of transmission fluid carried in the lines can be large compared to the volume displacement (e.g., travel) that the seal can achieve without rupture, the seal can include a seat on the transmission fluid side of the seal to prevent excess displacement of the seal beyond this safe limit. However, any damage to the transmission lines carrying the transmission fluid can circumvent this protection. Where the pressure of the surrounding environment is less than the pressure of the process fluid, damage to the lines containing the transmission fluid can provide an outlet for the transmission fluid to leak to the surrounding environment. Alternatively, where the pressure of the surrounding environment is greater than the pressure of the process fluid, any damage to the lines containing the transmission fluid can lead to rupture of the seal. Once the seal is ruptured, the transmission fluid, and potentially fluids from the surrounding environment, can mix with the process fluid. Furthermore, should the pressure of the surrounding environment decrease below that of the process fluid after the seal is ruptured, the transmission fluid, and possibly the process fluid itself, can leak to the surrounding environment.